This application claims the priority benefit of Japanese application serial no. 2000-094303, filed on Mar. 30, 2000.
1. Field of the Invention
This invention relates in general to a freon compressor used for devices such as air-conditioners, refrigerators, showcases or vending machines for juice etc.
2. Description of Related Art
Electromotor devices composed of a direct current (DC) motor are installed within freon compressors used for devices such as air-conditioners, refrigerators, or showcases. The electromotor device consists of a stator and a rotor, and stator windings are wired on the stator. The rotor is then rotated by applying voltages on the stator windings, thereby the electromotor device is driven to operate the freon compressor. FIGS. 13 and 14 show a conventional stator structure of an electromotor device. As shown in FIGS. 13 and 14, a number of teeth 102 are formed on the stator 101 in an equal distance manner, and stator windings 103 are wired across the teeth 102. FIG. 15 shows a distribution of the magnetic lines of force of the electromotor device. As shown in FIG. 15, the electromotive machine 100 serving as the electromotor device is a direct current (DC) motor, and there are four permanent magnets 105 arranged on the stator 104 in a substantially rectangular shape. The magnetic lines of force of each permanent magnet 105 pass through the teeth 102 in four directions, forming magnetic loops passing through the stator 101.
FIG. 16 shows a control circuit for the conventional electromotor device. As shown in FIG. 16, an alternating current (AC) power source is connected to a rectifier smoothing circuit 33 consisting of a rectifier diode D1 and a capacitor 35. The rectifier smoothing circuit 33 is further connected to an inverter circuit 36 consisting of a number of semiconductor switch devices, such as FET transistors SW1, SW2, SW3, SW4, SW5 and SW6. The outputs of the inverter circuit 36 are connected to the stator windings 103 of the electromotive machine 100 through three wirings 37, 38 and 39. Each of the wirings 37, 38 and 39 is respectively connected to a position detector 106 via a detecting circuit (not shown) that is used for voltages on the stator windings 103. In addition, the position detector 106 is further connected to the inverter circuit 36 through a tachometer 107 and an equi-width pulse width modulation (PWM) waveform generator 109. A conductive phase switch circuit 108 is connected between the position detector 106 and the inverter circuit 36.
The position detector 106 is used for detecting whether the wirings 37, 38 and 39 are applied voltages thereon by the inverter circuit 36, and then the rotation number of the rotor is calculated by the tachometer 107. According to the calculated rotation number, the equi-width PWM waveform generator 109 generates an equi-width PWM waveform to output to the inverter circuit 36. Afterwards, the inverter circuit 36 divides the equi-width PWM waveform into three phases (U phase, V phase and W phase) separated by 120 degrees, capable of respectively being transmitted on the wirings 37, 38 and 39. The inverter circuit 36 then outputs signals along two of the three wirings 37, 38 and 39, such that a magnetic field is generated on any one tooth 102 of the stator windings 103 for driving the electromotor 100 to operate the freon compressor. In addition, the conductive phase switch circuit 108 determines the outputs of the inverter circuit 36 based on the output of the position detector 105.
FIG. 17 shows operational modes of the electromotor. As shown in FIG. 17, the inverter circuit 36 outputs an equi-width PWM waveform (plus) using a KA1 mode to the U phase wiring (the wiring 37), and the equi-width PWM waveform (minus) to the V phase wiring (the wiring 38), by which a current is generated to flow along the black arrow and a magnetic force is generated along the white arrow. Next, the inverter circuit 36 outputs an equi-width PWM waveform (plus) using a KA2 mode to the U phase wiring (the wiring 38), and the equi-width PWM waveform (minus) to the W phase wiring (the wiring 39), by which a current is generated to flow along the black arrow and a magnetic force is generated along the white arrow.
Next, the inverter circuit 36 outputs an equi-width PWM waveform (plus) using a KA3 mode to the V phase wiring, and the equi-width PWM waveform (minus) to the W phase wiring, by which a current is generated to flow along the black arrow and a magnetic force is generated along the white arrow. The inverter circuit 36 outputs an equi-width PWM waveform (plus) using a KA4 mode to the V phase wiring, and the equi-width PWM waveform (minus) to the U phase wiring, by which a current is generated to flow along the black arrow and a magnetic force is generated along the white arrow. The inverter circuit 36 outputs an equi-width PWM waveform (plus) using a KA5 mode to the W phase wiring, and the equi-width PWM waveform (minus) to the U phase wiring, by which a current is generated to flow along the black arrow and a magnetic force is generated along the white arrow.
Next, the inverter circuit 36 outputs an equi-width PWM waveform (plus) using a KA6 mode to the W phase wiring, and the equi-width PWM waveform (minus) to the V phase wiring, by which a current is generated to flow along the black arrow and a magnetic force is generated along the white arrow. Accordingly, the magnetic force is sequentially rotated such that the rotor 104 is rotated. Thus, as shown in FIG. 18, a rotary magnetic field is generated in a manner that the circumference (an electric angle, equal to 360 degrees) is equally divided into six by releasing one of the three phases and then applying voltages on the other two phases for rotating the electromotor 100.
Therefore, according to the conventional method, the position detector is first used to detect a rotation position for detecting which one of the U-, V- and W-phases is released. For example, during the conductive status in the KA1 mode, only the magnetic field involving the rotor rotates, and the magnetic field involving the stator is not rotated, therefore, the distribution of the magnetic lines of force is more dense in space and time, causing a high magnetic flux of harmonic wave. The majority of noise results from this high magnetic flux of harmonic wave.
The object of this invention is to provide an electromotor device in which the distribution of the magnetic lines of forces are stabilized in space and time, and therefore to provide a freon compressor capable of significantly reduced noise.
Therefore, it is an objective of the present invention to provide a freon compressor. The freon compressor comprises a compressor device and an electromotor device. The electromotor device is used to drive the compressor device and consists of a stator and a rotor rotating within the stator. The stator further consists of a stator core and stator windings wired on the stator core, and a three-phase sine alternating current waveform is applied to the stator windings.
The rotor further comprises a rotor core and a plurality of permanent magnets formed within the rotor core. The permanent magnets are arranged in a substantially rectangular configuration. In addition, the permanent magnets can be also divided into four sets of parallel permanent magnets and these four sets of parallel permanent magnets are arranged on the rotor core. The rotor further comprises a rotor core and a plurality of permanent magnets arranged on the surface of the rotor core. The permanent magnets can be magnets made from rare-earth elements, or ferrite. The stator core further comprises at least six to twelve slots thereon, and the stator windings are directly wired on the slots. Freon absorbed and compressed by the compressor device comprises HFC freon or a natural freon. The compressor device comprises a rolling piston, a pump combining a pair of eddy devices, or a reciprocating piston. Furthermore, two to six magnetic poles can be formed in the rotor.
According to the present invention, the positions of the permanent magnets are not detected by a position sensor. As mentioned, the three-phase sine alternating current waveform is obtained by performing a quasi-sine wave pulse width modulation on a direct current (DC) power source. In addition, the three-phase sine alternating current waveform is obtained by superposing a third high harmonic wave thereon and then performing a quasi-sine wave pulse width modulation. The three-phase sine alternating current waveform is applied to control a torque for keeping a constant rotation speed of the rotor.